1. Field of the Invention
The present invention relates to an image display apparatus, an image display method, and an image display program adapted for compositing a projection image projected on a projection screen and a written image written on a writing screen, extracting the written image as electronic information, and processing the written image.
2. Description of the Related Art
In addition to having basic functions for displaying visual information such as characters, figures, and images on a display screen, an image display apparatus is starting to have interactive functions for enabling the apparatus to work closely with a user.
Such functions may have developed in view of the recent technological advancements in information processing apparatuses such as the computer which is used to configure the system of the image display apparatus. Also, the fact that the image display apparatus is often used in situations demanding efficient execution of complicated processes involving interactive operations by the user may have created incentives for developing such functions.
For example, in a situation where the image display apparatus is used in a conference or a seminar in which participants discuss the contents of the image information displayed on the display screen, the image display apparatus may desirably have a function for inputting information describing matters discussed during the course of the conference/seminar as electronic information in a personal computer which function may enable a participant to write information over the image information displayed on the display screen as is necessary in leading the discussion.
In view of such circumstances, image display apparatuses have been developed that are adapted to realize image display and image writing on the same screen and extract the written image as electronic information.
For example, Japanese Laid-Open Patent Publication No. 2005-71192 discloses an image display apparatus that uses an image capturing device such as a CCD camera to capture images of written characters and figures as electronic image information, determines a representative color based on the RGB value of the written image information, and performs color conversion of the written image information into the determined representative color to extract the written image information. Japanese Laid-Open Patent Publication No. 2005-354171 discloses an image display apparatus that measures the external light in the used environment, switches the color of a projected image of an image projecting apparatus such as a projector to black or white according to the measured external light, and changes the color of a written image in order to obtain a composite image including a high quality written image that is not influenced by external light.
However, the technique disclosed in Japanese Laid-Open Patent Publication No. 2005-71192 does not take into account variations in external light so that when the image display apparatus is used in a very dark environment (e.g., inside a room with the lights turned off) or a very bright environment (e.g., environment in which sunlight seeps through the display screen), the accuracy of color distinction involving determining a representative color based on the RGB value of a written image and distinguishing the written color may be degraded.
Also, although the technique disclosed in Japanese Laid-Open Patent Publication No. 2005-354171 takes into account the variations in external light in adjusting the color of a written image to thereby achieve advantageous effects in improving the quality of the composite image from which a written image is extracted (i.e., an image suitable for having written information extracted therefrom may be stably obtained under any usage environment), with regard to image processes for extracting the written image from the composite image (e.g., background removal, shading correction, color conversion), effective measures that take into account such variations in external light to accurately extract the written image are not proposed so that the accuracy of written image extraction may be degraded in such image processes including color distinction and recognition of the written image, for example.
As can be appreciated, prior art techniques as described above have problems with regard to accurately extracting a written image from a composite image taking into account variations in external light conditions that may vary depending on the usage environment of the image display apparatus.